Steam turbine and method for adjusting thrust forces thereof

ABSTRACT

A steam turbine having at least a HP blade cascade, an IP blade cascade and a plurality of dummy members that are attached to a common rotor shaft, is provided with, but not limited to, a detection unit that detects a steam flow into an IP chamber, a pressure reducing unit that reduces a pressure difference between both sides of a target dummy member of said plurality of the dummy members when the steam flow into the IP chamber stops, the target dummy member having one side communicating with a part of the IP chamber, and a control unit that controls the pressure reducing unit based on a detection result obtained by the detection unit.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a steam turbine and a method of adjusting a thrust force of the steam turbine, particularly regarding a steam turbine and a method of adjusting a thrust force of the steam turbine which are capable of balancing of a thrust force acting on a rotor shaft of the steam turbine which includes at least a high-pressure (HP) blade cascade, an intermediate-pressure (IP) blade cascade and a plurality of dummy members that are attached to a common rotor shaft.

Since the rotor shaft is subjected to the thrust force acting thereon, the steam turbine is provided with a thrust bearing. With a limited load capacity of the bearing, it is necessary to design the steam turbine in consideration of a thrust balance so that the thrust force acting on the rotor shaft does not exceed the load capacity of the bearing under any operating condition.

Hence, the dummy members (dummy pistons) and the blade cascades are attached to the same rotor shaft, so as thrust forces in a counter-thrust direction are generated by the dummy members to balance the forces acting in an axial direction of the entire rotor shaft. In this manner, the thrust force acting on the rotor shaft is kept within the scope of the load capacity of the bearing under any operation condition.

FIG. 13 shows an outline view regarding a conventional steam turbine under a normal operating condition, the conventional steam turbine being provided with dummy members for adjusting the thrust forces.

In a conventional steam turbine 1 depicted in FIG. 13, a turbine casing (not shown) is formed around a rotor shaft 10. The turbine casing includes an inlet part (not shown) for introducing high-pressure (HP) main steam 22, an inlet part (not shown) for introducing reheat steam 24 and an inlet part (not shown) for introducing low-pressure (LP) main steam 26.

Further, a HP blade cascade 2 to which the HP main steam is supplied, an IP blade cascade 4 to which the reheat steam 24 is supplied and a low-pressure (LP) blade cascade 6 to which the LP main steam 26 is supplied are attached to the rotor shaft 10 in this order. The IP blade cascade 4 and the LP blade cascade 6 have steam inlets that are open to one side, whereas the HP blade cascade 2 has a steam inlet is open to other side being opposite to the one side. Between the steam inlet of the HP blade cascade 2 and the steam inlet of the IP blade cascade 4, a high-pressure (HP) dummy member 12 is provided. On a steam outlet side of the HP blade cascade 2, an intermediate-pressure (IP) dummy member 14 and a low-pressure (LP) dummy member 16 are provided in this order. Further, a thrust balance conduit 30 is provided so as to communicate the outlet side of the IP dummy member 14 to a latter half of the IP blade cascade 4.

In the steam turbine 1 as described above, the HP main steam 22 from a boiler and the like (not shown) enters the HP blade cascade 2. And, the HP main steam 22 gives a rotary force to the rotor shaft 10 while the steam passes through the HP blade cascade 2. The steam that has done the work through the HP blade cascade 2 drops the pressure and the temperature gradually and is discharged out of the steam turbine 1 as a low-temperature reheat steam 28. The low-temperature reheat steam 28 discharged out of the steam turbine 1 is reheated by a reheat boiler (not shown) to be the reheat steam 24.

The IP reheat steam 24 that is reheated by the reheat boiler gives the rotary force to the rotor shaft 10 and gradually reduces the pressure and the temperature while the reheat steam 24 passes through the IP blade cascade 4. Further, the LP main steam 26 gives the rotary force to the rotor shaft 10 and gradually reduces the pressure and the temperature while the LP main steam 26 passes through the LP blade cascade 6.

Further, a part of the high-pressure (HP) main steam 22 passes by the high-pressure (HP) dummy member 12 and a part of the low-temperature reheat steam 28 that has passed through the HP blade cascade and has reduced the temperature and the pressure, passes by the intermediate-pressure (IP) dummy member 14 and the low-pressure (LP) dummy member 16.

Further, in FIG. 13, the thrust forces acting on the rotor shaft 10 at the cascades and the dummy members on the rotor shaft are represented by encircled numbers, 1 to 6 and an example regarding a set of the pressure values between adjacent pair of each blade cascade (dummy parts) are shown in FIG. 13. In addition, the thrust forces indicated by encircled numbers 1,2,3,4,5 and 6 denote the thrust forces acting on the LP dummy member 16, the IP dummy member 14, the HP blade cascade 2, the HP dummy member 12, the IP blade cascade 4 and the LP blade cascade 6, respectively. The thrust force acing on each of the blade cascades can be computed based on the gas pressure force working on each blade cascade and the thrust force acting on each of the dummy members can be computed based on a pressure difference between both sides of each dummy member and a cross-sectional area of each dummy member.

As shown in FIG. 13, the dummy members 12, 14 and 16, and the thrust balance conduit 30 are provided so as to balance the thrust forces by the steam pressure. In other words, the thrust force acting on the HP dummy member 12 roughly serves as a counterbalance to the thrust force acting on the HP blade cascade 2, the thrust acting on the IP dummy member 14 roughly serving as a counterbalance to the thrust force acting on the IP blade cascade 4, the thrust force acting on the LP dummy member 16 roughly serving as a counterbalance to the thrust force acting on the LP blade cascade 6. Thus, the resultant thrust force acting on the whole steam turbine 1 is balanced.

Further, in the steam turbine, in order to prevent the thrust bearing from being damaged, the resultant thrust force needs to be brought into balance not only in a case where the steam turbine is operated under a normal operating condition but also in a case where either the HP main steam supply or the reheat steam supply is stopped.

First, attention is paid to a case where the flow of the HP main steam 22 through the steam turbine 1 as shown in FIG. 13 is stopped due to a trouble, a tuning operation or the like. FIG. 14 shows the outline of the state of the steam turbine provided with conventional dummy parts for adjusting thrust balance, when the supply of the HP main steam 22 is stopped.

As shown in FIG. 14, when the supply of the HP main steam 22 is stopped, the flow of the steam streaming through the HP blade cascade 2 stops, causing the pressure difference of the HP blade cascade to be 0. Accordingly, the thrust force represented by the encircled numeral 3 as depicted in FIG. 14 also becomes 0. Further, the pressure difference of the HP dummy member 12 becomes infinitesimal and, the thrust force represented by the encircled numeral 4 becomes approximately 0. Therefore, as shown in FIG. 14, the resultant thrust force developed in the whole steam turbine 1 is substantially balanced, even in a case where the supply of the HP main steam 22 is stopped.

In the next place, attention is paid to a case in which the flow of the reheat steam 24 and the LP main steam 26 through the steam turbine 1 as shown FIG. 13 is stopped due to a trouble, a tuning operation or the like. FIG. 15 shows the outline of the state of the steam turbine provided with conventional dummy parts for adjusting thrust balance, when the supply of the reheat steam and the LP main steam is stopped.

As shown in FIG. 15, when the supply of the reheat steam 24 and the LP main steam 26 is stopped, the flow of the steam streaming through the IP blade cascade 4 and the LP blade cascade 6 ends. Each of the pressures on both sides of the IP blade cascade 4 and the pressures on both sides of the LP blade cascade 6 becomes approximately a level of vacuum pressure. Further, due to the thrust balance conduit 30 that communicates the IP dummy member 14 to the latter half of the IP blade cascade 4, the pressure between the IP dummy member 14 and the LP dummy member 16 also becomes a level of vacuum pressure.

In such case, in an LP system (a low-pressure part of the steam turbine), the pressure difference between both sides of the LP blade cascade 6 and the pressure difference between both sides of the LP dummy member 16 become approximately 0, resulting in the thrust force acting on the rotor shaft being 0.

Further, in relation to the IP system (the intermediate-pressure part of the steam turbine), the pressure at the outlet of the IP dummy member 14 becomes a level of vacuum pressure and in response to the vacuum pressure level, the thrust force represented by the encircled numeral 2 as shown in FIG. 15 increases. In addition, the pressure difference between both sides of the IP blade cascade 4 becomes approximately 0. In this manner, the thrust force represented by the encircled numeral 5 becomes approximately 0. As a result, the resultant thrust force acting toward the direction of the IP dummy member side (leftward in FIG. 15) increases.

Further, in relation to a HP system (a high-pressure part of the steam turbine), the thrust force generated in the HP blade cascade 2 represented by the encircled numeral 3 is approximately the same as that of a normal operation condition, whereas the thrust force represented by the encircled numeral 2 generated in the HP dummy member 12 increases by an amount corresponding to the vacuum pressure level at the outlet of the HP dummy member 12. Thus, the thrust force acting in the direction of the HP dummy member (rightward in FIG. 15) increase.

Hereby, the increase of the thrust force generated in the IP system is greater than the increase of the thrust force generated in the HP system. Accordingly, the resultant thrust force generated in the whole steam turbine 1 increases in the leftward direction in FIG. 15. Thus, the resultant thrust force acting on the whole steam turbine is not balanced.

In a case where the flow of the reheat steam 24 is stopped, it may be considered that the HP dummy member 12 is upsized so that thrust force in the rightward direction increases and the resultant thrust force is balanced. However, the upsizing of the HP dummy member 12 spoils the balancing in the normal operation and thus, this approach is not appropriate.

Hence, in relation to each of FIG. 13 to FIG. 15, the IP dummy member 14 is downsized and the LP dummy member 16 is upsized. By this, the balance of the thrust force can be maintained under the normal operating condition, even in a case where the supply of any one of the HP main steam and the reheat steam is stopped.

In addition, Patent Reference 1 discloses another technology; according to this technology, thrust forces acting on the steam turbine are evaluated based on the measured data such as bearing temperatures. Based on the results of the measurements, the thrust forces acting on the dummy members can be adjusted in an electronic control approach, and the resultant thrust force developed in the whole steam turbine is brought into balance.

REFERENCES Patent References

Patent Reference 1: JP1996-189302

SUMMARY OF THE INVENTION Subjects to be Solved

In the conventional technology as explained above in reference to FIG. 13 through FIG. 15, it is necessary to downsize the IP dummy member 14 and upsize the LP-dummy member 16 so as to balance the resultant thrust force even when the supply of the reheat steam in addition to the HP main steam is stopped in the normal operation. Upsizing of the LP dummy member 16 accompanies upsizing of the casing that is located at the outer periphery of the LP dummy member 16. Accordingly, the whole steam turbine 1 is inevitably upsized and the manufacturing cost increases. Moreover, when the diameter of the LP dummy member 16 is increased, the steam leakage from the LP dummy member 16 toward the gland increases. Inevitably, there arises a possibility that the performance of the steam turbine 1 deteriorated. In recent years, the LP blade cascade is becoming larger, accompanying upsizing of the LP dummy member. However, it is not desirable to upsize the LP dummy member to balance the thrust forces.

Further, in the technology as disclosed by Patent Reference 1 where the balancing of the thrust forces is performed by use of an electric control, there is a possibility that the reliability of the electric system may cause a problem.

In view of the above problems of the related art, it is an object of the present invention to provide a steam turbine and a method of adjusting a thrust force of the steam turbine acting on a rotor shaft of the turbine in an entire operating range of the steam turbine without upsizing a LP dummy member or without using an electric control of a complicated system.

Means to Solve the Subjects

To solve the above issues, the present invention provides a steam turbine having at least a high-pressure (HP) blade cascade, an intermediate-pressure (IP) blade cascade and a plurality of dummy members that are attached to a common rotor shaft. The steam turbine may include, but is not limited to:

a detection unit that detects a steam flow into an intermediate-pressure (IP) chamber;

a pressure reducing unit that reduces a pressure difference between both sides of a target dummy member of said plurality of the dummy members when the steam flow into the IP chamber stops, the target dummy member having one side communicating with a part of the IP chamber; and

a control unit that controls the pressure reducing unit based on a detection result obtained by the detection unit.

In this manner, the thrust force generated at the IP dummy member when the steam flow into the IP chamber stops can be eliminated. Thus, it is no longer necessary to increase the diameter of the LP dummy member which was conventionally needed to balance the thrust force generated at the IP dummy member. As a result, the diameter of the LP dummy member can be reduced and the thrust forces acting on the rotor of the steam turbine can be balanced in the entire operation range of the steam turbine without using the electric control of the complicated system.

The above pressure reducing unit may include, but is not limited to, a first conduit that connects the both sides of the target dummy member and a first valve that is provided in the first conduit to adjust the pressure difference between the both sides of the target dummy member.

In this way, the thrust forces acting on the rotor shaft of the steam turbine can be balanced, with a simple configuration.

The above steam turbine may further include:

a third conduit that connects the one side of the pressure reducing unit to an outlet of the IP chamber; and

a third valve that is provided in the third conduit.

When the first valve opens while the steam flow into the IP chamber is not stopped, the control unit may control the third valve to open so as to generate the pressure difference between the both sides of the target dummy member.

In this way, even when the first valve is out of order, the thrust forces generated in the steam turbine can be balanced and, the reliability of the steam turbine can be enhanced.

The above pressure reducing unit may include, but is not limited to:

a second conduit that connects the part of the IP chamber and the one side of the target dummy member; and

a second valve that is provided in the second conduit to adjust the difference between the both sides of the target dummy member.

The second valve may be closed when the steam flow into the IP chamber stops.

In relation to the above, the second conduit is often provided even in the conventional steam turbines. Thus, in remodeling or modernizing the conventional existing steam turbine, the pressure reducing unit can be provided by simply fitting the second valve to the existing second conduit without newly installing a conduit to the steam turbine. Thus, the remodeling can be easily accomplished.

The above steam turbine may further include:

a bypass conduit that is provided to bypass the second valve; and

an orifice that is provided in the bypass conduit.

In this way, the thrust forces generated in the steam turbine can be easily balanced.

The above steam turbine may also include:

a third conduit that connects the one side of the pressure reducing unit to an outlet of the IP chamber; and

a third valve that is provided in the third conduit.

When the second valve closes while the steam flow into the IP chamber is not stopped, the control unit may control the third valve to open so as to generate the pressure difference between the both sides of the target dummy member.

To achieve the object of the present invention, the present invention provides a method of adjusting a thrust force of a steam turbine having at least a HP blade cascade, an IP blade cascade and a plurality of dummy members that are attached to a common rotor shaft. The method may include, but is not limited to, the step of reducing a pressure difference between both sides of a target dummy member of said plurality of the dummy members when the steam flow into the IP chamber stops, the target dummy member having one side communicating with a part of the IP chamber.

Further, in the above method, the pressure difference between the both sides of the target dummy member may be reducible by use of a first valve provided in a first conduit that connects the both sides of the target dummy member.

Further, in the above method, when the first valve opens while the steam flow into the IP chamber is not stopped, the pressure difference may be generated between the both sides of the target dummy member by opening a third valve which is provided in a third conduit that connects the one side of the target dummy member to an outlet of the IP chamber.

In the above method of adjusting the thrust force of the steam turbine, the pressure difference between the both sides of the target dummy member may be reducible by use of a second valve provided in a second conduit that connects the part of the IP chamber and the one side of the target dummy member.

In the above method of adjusting the thrust force of the steam turbine, when the second valve closes while the steam flow into the IP chamber is stopped, the pressure difference may be generated between the both sides of the target dummy member by opening a third valve which is provided in a third conduit that connects the one side of the target dummy member to an outlet of the IP chamber.

EFFECTS OF THE INVENTION

According to the present invention, the steam turbine and the method of adjusting the thrust force of the steam turbine can be provided which are operable to balance the thrust forces in the entire operation range of the steam turbine without upsizing the LP dummy member, as well as, without using the electric control of a complicated system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of a single-casing reheat steam turbine provided with a plurality of dummy members for adjusting thrust forces, according to a first preferred embodiment of the present invention.

FIG. 2 shows an outline of a normal operating state of the steam turbine provided with the dummy members for adjusting thrust forces, according to the first preferred embodiment of the present invention.

FIG. 3 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces when the supply of the HP main steam is stopped, according to the first preferred embodiment of the present invention.

FIG. 4 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces when the supply of the reheat steam and the LP main steam is stopped, according to the first preferred embodiment of the present invention.

FIG. 5 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces in a case where a valve is in an abnormal condition in the normal operating state of the steam turbine, according to the first preferred embodiment of the present invention.

FIG. 6 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces, after taking a countermeasure against the malfunction of the valve in the normal operating state of the steam turbine, according to the first preferred embodiment of the present invention.

FIG. 7 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces in a case where another valve is in an abnormal condition in the normal operating state of the steam turbine, according to the first preferred embodiment of the present invention.

FIG. 8 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces, after taking a countermeasure against the malfunction of said another valve in the normal operating state of the steam turbine, according to the first preferred embodiment of the present invention.

FIG. 9 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces, according to the first preferred embodiment of the present invention, in a case where the function of a valve is out of order while the supply of the reheat steam and the LP main steam is stopped.

FIG. 10 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces, according to the first preferred embodiment of the present invention, after taking a countermeasure against the malfunction of the valve while the supply of the reheat steam and the LP main steam is stopped.

FIG. 11 shows an outline of a HP-IP steam turbine provided with the dummy members for adjusting thrust forces, according to a second preferred embodiment of the present invention.

FIG. 12 shows an outline of a HP-IP steam turbine provided with the dummy members for adjusting thrust forces, according to a third preferred embodiment of the present invention.

FIG. 13 shows an outline of a normal operating state of the steam turbine provided with conventional dummy members.

FIG. 14 shows an outline of a state of the steam turbine provided with conventional dummy parts for adjusting thrust balance, when the supply of the HP main steam is stopped.

FIG. 15 shows an outline of a state of the steam turbine provided with conventional dummy parts for adjusting thrust balance, when the supply of the reheat steam and the LP main steam is stopped.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, shape, its relative positions and the like shall be interpreted as illustrative only and not limitative of the scope of the present invention.

PREFERRED EMBODIMENTS First Preferred Embodiment

FIG. 1 shows a configuration of a single-casing reheat steam turbine provided with a plurality of dummy members for adjusting thrust forces, according to a first preferred embodiment of the present invention. In a steam turbine shown in FIG. 1, a low-pressure (LP) casing 32 and a HP-IP casing 34 (a high-intermediate-pressure casing) are formed around a rotor shaft 10. The HP-IP casing 34 is provided with a high-pressure (HP) steam inlet 23 through which HP steam 22 is supplied to the steam turbine and a reheat steam inlet 25 through which reheat steam 24 is supplied to the steam turbine. Further, the LP casing 32 is provided with a low-pressure (LP) steam inlet 27 through which LP steam 26 is supplied to the steam turbine.

To the rotor shaft 10, attached are a HP blade cascade 2 to which the HP main steam is supplied, an intermediate-pressure (IP) blade cascade 4 to which the reheat steam 24 is supplied and a low-pressure (LP) blade cascade 6 to which the LP main steam 26 is supplied in this order.

In the steam turbine, steam inlet sides of the IP blade cascade 4 and the LP blade cascade 6 are arranged such that the steam streams through the IP blade cascade 4 and the LP blade cascade 6 in the same direction, whereas a steam inlet side of the HP blade cascade 2 is arranged such that the steam streams through the HP blade cascade 2 in the opposite direction. Further, a HP dummy member 12 is provided between the steam inlet side of the HP blade cascade 2 and the steam inlet side of the IP blade cascade 4. On the steam outlet side of the HP blade cascade 2, an IP dummy member 14 and a LP dummy member 16 are provided in this order. Furthermore, a thrust balance conduit 30 is provided to communicate the steam outlet side of the IP dummy member 14 to a part of the IP blade cascade 4.

FIG. 2 shows an outline of a normal operating state of the steam turbine provided with the dummy members for adjusting thrust forces. Hereby, the same components in FIG. 2 as in FIG. 1, FIG. 13 through FIG. 15 are given common numerals and are not explained further. Herein, a normal operating state means an operating state of the steam turbine in which all of the HP steam 22, the reheat steam 24 and the LP steam 26 are supplied to the steam turbine.

Differently from the conventional technology shown in FIG. 13, in the first preferred embodiment of the present invention as shown in FIG. 2, the diameter of the IP dummy member 14 is upsized in comparison with the conventional dummy member 14, whereas the diameter of the LP dummy member 16 is downsized in comparison with the conventional dummy member 16. With the LP dummy member 16 having larger diameter, the thrust forces of the steam turbine as a whole are prevented from being unbalanced.

Further, a conduit 42 is provided to communicate the steam inlet side of the IP dummy member 14 to the steam outlet side thereof and a valve 43 is provided on the conduit 42. A conduit 44 is connected to the conduit 42 on a side closer to the steam outlet side of the IP dummy part than the valve 43 and in communication to the steam outlet side of the IP blade cascade 4. A valve 45 is provided on the conduit 44. A valve 41 is provided on the thrust balance conduit 30.

Further, a control unit 52 is provided. The control unit 52 reads a detected value detected by a pressure sensor 54 which is provided at the reheat steam inlet 25 and controls opening and closing of the valves 41, 43 and 45 based on the detected value. In the normal operating state where the reheat steam 24 is supplied to the steam turbine 1 and the pressure detected by the pressure sensor 54 is within a normal pressure range of the reheat steam 24, the control unit 52 controls the valve 41 to open and the valves 43 and 45 to close as shown in FIG. 2. As for the open-close state of the valves in the attached drawings, the valve mark filled in with black indicates an opened state, whereas the valve mark filled in with white indicates a closed state.

In FIG. 2 through FIG. 10 and FIG. 13 through FIG. 15, the unit k denotes a pressure value in kgf/cm² to show pressure values as only example values at indicated places.

As shown in FIG. 2, the steam turbine is provided with the dummy members 12, 14 and 16, and the thrust balance conduit 30. In the normal operating state, the resultant thrust force generated by the steam pressures is balanced.

Next, a case where the supply of the HP main steam 22 is stopped in the steam turbine 1 shown in FIG. 2 is explained. FIG. 3 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces of the present invention when the supply of the HP main steam is stopped. In FIG. 3 through FIG. 15, the control unit 52 is omitted.

In FIG. 3, when the supply of the HP main steam 22 is stopped, no steam is supplied to the HP blade cascade 2, and the pressure difference at the HP blade cascade 2 becomes 0. Thus, the thrust force represented by the encircled numeral 3 as depicted in FIG. 14 also becomes 0. Accordingly, the pressure difference at the HP dummy member 12 becomes significantly small and the thrust force represented by the encircled numeral 4 becomes close to 0. Therefore, as shown in FIG. 3, even when the supply of the HP main steam 22 is stopped, the resultant thrust force acting on the whole steam turbine 1 is balanced.

Next, a case where the supply of the reheat steam 24 and the LP main steam 26 is stopped in the steam turbine 1 shown in FIG. 2 is explained. FIG. 4 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces of the present invention when the supply of the reheat steam and the LP main steam is stopped.

In FIG. 4, when the supply of the reheat steam 24 and the LP main steam 26 is stopped, no steam is supplied to the IP blade cascade 4 and the LP blade cascade 6. This causes the pressures at both sides of the IP blade cascade 4 and the LP blade cascade 6 to be approximately at vacuum level. In the HP system (the high-pressure part of the steam turbine), the thrust force represented by the encircled numeral 3 generated at the HP blade cascade 2 is almost the same as the thrust force in the normal operating state of the steam turbine. However, the thrust force represented by the encircled numeral 2 generated at the HP dummy member 12 increases in response to the increase regarding the level of the vacuum pressure at the outlet of the HP dummy member 12. By this, the thrust force acting on the HP dummy member 12 increases in the direction of the steam flow along the HP dummy member (in the rightward direction in FIG. 4).

When the control unit 52 (not shown in FIG. 4) determines that the reheat steam 24 is not supplied based on the pressure value detected by the pressure sensor 54 (not shown in FIG. 4), the control unit 52 opens the valve 43. By this, the pressure difference between both sides of the IP dummy member 14 becomes approximately 0. Specifically, in a case where the reheat steam 24 is not supplied to the steam turbine in the conventional technology, an excessive thrust force is generated at the IP dummy member 14 in the leftward direction. On the other hand, in this preferred embodiment of the present invention, the thrust force can be prevented from being generated at the IP dummy member 14.

Further, in the case of FIG. 4, the diameter of the LP dummy member 16 is designed so as to generate a counter thrust force (leftward in FIG. 4) approximately by an amount corresponding to the above-described increased thrust force generated in the HP system. Thus, the thrust force generated in the whole steam turbine 1 is balanced.

In addition, the diameter of the LP dummy member 16 is designed in advance so as to balance the thrust forces in a case where the valves 41 and 43 are opened in the state where the supply of the reheat steam and the LP main steam is stopped and, the diameter of the IP dummy member 14 is designed in advance so as to balance the thrust forces in the normal operating state and the state where the supply of the HP main steam is stopped. In this way, the thrust force is prevented from being generated at the IP dummy member 14 when the supply of the reheat steam and the LP main steam is stopped, and it becomes unnecessary to upsize the diameter of the LP dummy member 16, apart from the conventional technology in which the diameter upsizing was inevitable. Hence, the diameter of the LP dummy member 16 can be small and the steam leakage to the gland can be reduced. As a result, the performance of the steam turbine can be enhanced.

Next, the countermeasures against the possible abnormal-conditions that may be caused by providing the valves 41, 43 and 45 are explained.

First, abnormal conditions of the valve 43 are now explained.

FIG. 5 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces of the present invention in a case where the valve 43 is in an abnormal condition in the normal operating state of the steam turbine.

In FIG. 5, when the valve 43 becomes out of order due to a fault and so on, the valve 43 is opened and then both sides of the IP dummy member 14 are in communication with each other, and the pressure at the steam outlet side of the IP dummy member 14 increases. And, the pressure difference between both sides of the IP dummy member 14 becomes almost 0. Thus, the thrust force generated at the IP dummy member 14 becomes almost 0. As a result, the resultant thrust force of the whole steam turbine 1 becomes unbalanced.

In the event as described above, the pressure detected by a pressure sensor 56 provided in the thrust balance conduit 30 increases. When the detected pressure value exceeds a prescribed value, then the control unit 52 (not shown in FIG. 5) determines that the valve 43 or 41 is not working properly.

Once it is determined that the valve 43 or 41 is not working properly, the control unit 52 opens the valve 45.

FIG. 6 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces of the present invention, after taking a countermeasure against the malfunction of the valve 43 in the normal operating state of the steam turbine.

When the control unit 52 opens the valve 45, the steam outlet side of the IP dummy member 14 communicates with the steam outlet side of the IP blade cascade 4 via the conduit 44. A part of the steam at the steam outlet side of the IP dummy member 14 streams to the steam outlet side of the IP blade cascade 4. This causes the pressure at the steam outlet side of the IP dummy member 14 to drop so that the pressure difference between both sides of the IP dummy member 14 is generated, thereby generating the thrust force at the IP dummy member 14. As a result, the resultant thrust force generated in the whole steam turbine 1 is balanced. In addition, it is necessary to design the conduits 44 and the valve 45 in advance so that the steam flow rate through the conduit 44 is almost the same as the steam flow rate through the valve 43 when the valve 45 is opened in a case when the valve 43 is abnormally opened.

As described above, even when the valve 43 is in the abnormal condition, the resultant thrust force can be kept balanced; thus, the reliability of the steam turbine 1 can be enhanced with additionally provided simple-components.

Next, the abnormal-conditions of the valve 41 are explained.

FIG. 7 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces of the present invention in a case where the valve 41 is in an abnormal condition in the normal operating state of the steam turbine.

In FIG. 7, when the valve 41 becomes out of order because of a fault and so on and the valve 41 is closed, then the steam at the outlet side of the IP dummy member 14 is no longer able to stream toward the IP blade cascade 4 through the thrust balance conduit 30. On the other hand, when there is a pressure difference between both sides of the IP dummy member 14, the steam in a labyrinth seal provided at an outer periphery of the IP dummy member 14 leaks toward the steam outlet side thereof. Thus, the pressure difference between both sides of the IP dummy member 14 becomes approximately 0. Accordingly, the thrust force acting on the IP dummy member 14 becomes approximately 0. As a result, the resultant force is unbalanced.

In the event as described above, the pressure detected by the pressure sensor 56 provided on the thrust balance conduit 30 increases. When the detected pressure exceeds a prescribed value, then the control unit 52 (not shown in FIG. 5) determines that the valve 43 or 41 is not working properly.

Once it is determined that the valve 43 or 41 is not working properly, the control unit 52 opens the valve 45.

FIG. 8 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces of the present invention, after taking a countermeasure against the malfunction of the valve 41 in the normal operating state of the steam turbine.

When the control unit 52 opens the valve 45, the steam outlet side of the IP dummy member 14 communicates with the steam outlet side of the IP blade cascade 4 via the conduit 44. Then, a part of the steam at the steam outlet side of the IP dummy member 14 streams into the steam outlet side of the IP blade cascade 4. Thus, the pressure at the steam outlet side of the IP dummy member 14 drops so that the pressure difference between both sides of the IP dummy member 14 is generated. Accordingly, the thrust force is generated at the IP dummy member 14 so that the resultant thrust force generated in the whole steam turbine 1 is balanced.

As described above, even when the abnormal condition of the valve 41 happens, the resultant thrust force is kept balanced. Thus, the reliability of the steam turbine can be enhanced with additional simple-components.

Next, abnormal-conditions that may occur on the valve 41 in a case where the supply of the reheat steam and the LP main steam is stopped are explained.

FIG. 9 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces of the present invention, in a case where the function of the valve 43 is out of order while the supply of the reheat steam and the LP main steam is stopped

As described already based on FIG. 3, it is necessary to open the valve 43 in the case where the supply of the reheat steam and the LP main steam is stopped. However, FIG. 9 shows the case where the valve 43 stays closed.

In FIG. 9, with the valve 43 being closed, both sides of the IP dummy member 14 are not in communication with each other. Thus, the pressure difference between both sides of the IP dummy member 14 is generated so that the thrust force is generated at the dummy member 14. The thrust force generated at the dummy member 14 causes the resultant thrust force generated in the whole steam turbine 1 to be unbalanced. In the present invention, the diameter of the IP dummy member 14 is greater than that of the conventional IP dummy member. For a corresponding amount, the unbalance (i.e. being out of balance) regarding the developed resultant thrust force increases.

In the event as described above, the pressure detected by the pressure sensor 56 provided on the thrust balance conduit 30 drops. When the detected pressure value is processed below a prescribed value, then the control unit 52 (not shown in FIG. 9) determines that the valve 43 is not working properly.

Once it is determined by the control unit 52 that the valve 43 is not working properly, the control unit 52 closes the valve 41.

FIG. 10 shows an outline of a state of the steam turbine provided with the dummy members for adjusting thrust forces of the present invention, after taking a countermeasure against the malfunction of the valve 43 while the supply of the reheat steam and the LP main steam is stopped.

With the valve 41 being closed, the pressure difference between both sides of the IP dummy member 14 becomes approximately 0 due to the steam leakage from the IP dummy member 14. Accordingly, the thrust force acting on the IP dummy member 14 becomes almost 0.

In this manner, the resultant thrust force is balanced as is the case with FIG. 4 in which there is no abnormal condition regarding the valve 43.

Specifically, the resultant force is kept balanced, even when the abnormal condition regarding the valve 43 takes place.

Second Preferred Embodiment

The disclosed technology of the present invention is also applicable to HP-IP steam turbines.

FIG. 11 shows an outline of a HP-IP steam turbine provided with the dummy members for adjusting thrust forces according to a second preferred embodiment of the present invention.

The HP-IP steam turbine 101 depicted in FIG. 11 is provided with a turbine casing (not shown) is formed around a rotor shaft (not shown). The turbine casing encloses the inlet parts (not shown) for introducing HP steam and IP steam.

Further, a high-pressure (HP) chamber blade cascade 102 to which the HP steam is supplied and an intermediate-pressure (IP) chamber blade cascade 104 to which the IP steam is supplied are attached to the rotor shaft such that steam inlets of the HP chamber blade cascade 102 and the IP chamber blade cascade 104 are disposed facing each other. Further, between the steam inlet of the HP chamber blade cascade 2 and the steam inlet the IP chamber blade cascade 104, a first dummy member 111 and a second dummy member 112 are provided. Further, a third dummy member 113 is provided at a steam outlet of the HP chamber blade cascade 102. Further, a balance conduit 121 is provided to communicate a location between the first dummy member 111 and the second dummy member 112 to both sides of the third dummy member 113. Furthermore, a balance conduit 122 is provided to communicate the steam outlet of the third dummy member 113 to the steam outlet of the IP chamber blade cascade 104. In addition, a valve 141 is provided on the balance conduit 121 between both sides of the third dummy member 113 and the downstream side of the third dummy member 113 and a valve 142 is provided on the balance conduit 122.

In relation to the HP-IP steam turbine as described above, the table in FIG. 11 summarizes a balance of the thrust forces of the cases, when the turbine is operated normally, the supply of the HP steam is stopped (the HP system is closed), and the IP steam is stopped (the IP system is closed). The figures of the thrust forces in the table of FIG. 7 show not the absolute values but the relative ratios among thrust forces appearing in design calculations.

As shown in FIG. 7, in the normal operation state, the resultant thrust force is substantially balanced when the HP system is closed. In contrast, when the IP system is closed, the resultant thrust force becomes unbalanced because of the thrust force acting on the third dummy member 113 and the resultant thrust force increases rightward. In this event, when the valve 41 (CV1) is opened, the pressure difference between both sides of the third dummy member 113 is reduced and thus, the resultant thrust force generated in the whole steam turbine can be balanced. In addition, when the IP system is closed, the pressure difference between both sides of the third dummy member 113 can be also reduced via the steam leakage through the dummy member 113, by appropriately closing the valve 142 instead of opening the valve 141. As a result, the resultant thrust force generated in the whole steam turbine can be balanced.

Third Preferred Embodiment

FIG. 12 shows an outline of the HP-IP steam turbine provided with the dummy members for adjusting thrust forces according to a third preferred embodiment of the present invention.

The same components in FIG. 12 as in FIG. 11 are given common numerals and are not explained further.

In FIG. 12, a first dummy member 111′ is provided. The first dummy member 111′ is formed by integrating the first dummy member 111 and the second dummy member 112 (shown in FIG. 11), whose diameter is as same as the diameter of the first dummy member 111. Hereby, the steam turbine in FIG. 12 is not provided with the balance conduit 121. Instead, the balance conduit 122 is provided with a bypass conduit 123 that bypasses the valve 142. Further, an orifice 124 is provided on the bypass conduit 123.

In a manner similar to the second preferred embodiment, the resultant thrust force can be balanced, except when the IP system is closed. When the IP system is closed, the resultant thrust force can be balanced by adjusting the opening of the valve 142.

In the above event, when it is difficult to adjust the opening of the valve such as setting the opening of the valve 142 at a minimal level, it is recommendable to close the valve 42 and use the orifice 123. In relation to this event, it is necessary to set the size of the orifice in advance so that with the valve 142 being full-closed, the steam pressure at a back side of the third dummy member 113 is appropriate.

In other words, in a case where the IP system is closed, the valve 142 is closed and the steam streams through the orifice 124. Thus, the steam pressure at the back side of the third dummy member 113 is appropriately maintained. Hence, the resultant thrust force can be balanced.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a steam turbine and a method of adjusting a thrust force of the steam turbine acting on a rotor shaft of the turbine in an entire operating range of the steam turbine without upsizing a LP dummy member or without using an electric control of a complicated system. 

1. A steam turbine having at least a high-pressure blade cascade, an intermediate-pressure blade cascade and a plurality of dummy members that are attached to a common rotor shaft, the steam turbine comprising: a detection unit that detects a steam flow into an intermediate-pressure chamber; a pressure reducing unit that reduces a pressure difference between both sides of a target dummy member of said plurality of the dummy members when the steam flow into the intermediate-pressure chamber stops, the target dummy member having one side communicating with a part of the intermediate-pressure chamber; and a control unit that controls the pressure reducing unit based on a detection result obtained by the detection unit.
 2. The steam turbine according to claim 1, wherein the pressure reducing unit comprises: a first conduit that connects the both sides of the target dummy member; and a first valve that is provided in the first conduit to adjust the pressure difference between the both sides of the target dummy member.
 3. The steam turbine according to claim 2, further comprising: a third conduit that connects the one side of the pressure reducing unit to an outlet of the intermediate-pressure chamber; and a third valve that is provided in the third conduit, wherein, when the first valve opens while the steam flow into the intermediate-pressure chamber is not stopped, the control unit controls the third valve to open so as to generate the pressure difference between the both sides of the target dummy member.
 4. The steam turbine according to claim 1, wherein the pressure reducing unit comprises: a second conduit that connects the part of the intermediate-pressure chamber and the one side of the target dummy member; and a second valve that is provided in the second conduit to adjust the difference between the both sides of the target dummy member, wherein the second valve is closed when the steam flow into the intermediate-pressure chamber stops.
 5. The steam turbine according to claim 4, further comprising: a bypass conduit that is provided to bypass the second valve; and an orifice that is provided in the bypass conduit.
 6. The steam turbine according to claim 4, further comprising: a third conduit that connects the one side of the pressure reducing unit to an outlet of the intermediate-pressure chamber; and a third valve that is provided in the third conduit, wherein, when the second valve closes while the steam flow into the intermediate-pressure chamber is not stopped, the control unit controls the third valve to open so as to generate the pressure difference between the both sides of the target dummy member.
 7. A method of adjusting a thrust force of a steam turbine having at least a high-pressure blade cascade, an intermediate-pressure blade cascade and a plurality of dummy members that are attached to a common rotor shaft, the method comprising the step of: reducing a pressure difference between both sides of a target dummy member of said plurality of the dummy members when the steam flow into the intermediate-pressure chamber stops, the target dummy member having one side communicating with a part of the intermediate-pressure chamber.
 8. The method of adjusting the thrust force of the steam turbine according to claim 7, wherein the pressure difference between the both sides of the target dummy member is reducible by use of a first valve provided in a first conduit that connects the both sides of the target dummy member.
 9. The method of adjusting the thrust force of the steam turbine according to claim 8, wherein, when the first valve opens while the steam flow into the intermediate-pressure chamber is not stopped, the pressure difference is generated between the both sides of the target dummy member by opening a third valve which is provided in a third conduit that connects the one side of the target dummy member to an outlet of the intermediate-pressure chamber.
 10. The method of adjusting the thrust force of the steam turbine according to claim 7, wherein the pressure difference between the both sides of the target dummy member is reducible by use of a second valve provided in a second conduit that connects the part of the intermediate-pressure chamber and the one side of the target dummy member.
 11. The method of adjusting the thrust force of the steam turbine according to claim 10, wherein, when the second valve closes while the steam flow into the intermediate-pressure chamber is stopped, the pressure difference is generated between the both sides of the target dummy member by opening a third valve which is provided in a third conduit that connects the one side of the target dummy member to an outlet of the intermediate-pressure chamber. 